1. Field of the Invention
The present invention relates to a driving device using an electro-mechanical conversion element.
2. Description of the Related Art
Hitherto, a driving device employing a piezoelectric element (electro-mechanical conversion element), which is used to drive a lens of a digital camera or a camera phone, has been known. Such a driving device is configured so that one of end portions in the expansion/contraction direction of the piezoelectric element is fixed by a platform, and that a shaft-like driving frictional member extending in the expansion/contraction direction of the piezoelectric element is fixed to the other end portion of the piezoelectric element. A frictional engagement member capable of moving along the driving frictional member is mounted on the circumferential surface of the driving frictional member by being inserted thereon. The lens serving as a driven member is attached thereto through the frictional engagement member.
The frictional engagement member has a slider that has a through-hole, through which the driving frictional member is inserted, and also has a frictional member pressed against the circumferential surface of the driving frictional member exposed from a concave portion of the slide, and a plate spring adapted to press the frictional member. The frictional engagement member is engaged with the driving frictional member by fixing the plate spring with screws to a desired frictional force.
In such a driving device, the piezoelectric element is expanded or contracted by applying a pulse-like voltage to the piezoelectric element. Thus, the driving frictional member moves. In a case where the piezoelectric element deforms at a low rate, the frictional engagement member moves together with the driving frictional member. In a case where the piezoelectric element deforms at a high rate, the frictional engagement member remains located at the same position due to inertia of the masses of the frictional engagement member and the driven member, whereas the driving frictional member moves. Therefore, the frictional engagement member frictionally engaged with the driving frictional member intermittently moves with fine pitches. Thus, the lens attached to the frictional engagement member can be moved (see, for example, JP-A-2002-142470).
However, according to related art described in JP-A-2002-142470, a frictional engagement member includes a plurality of components. Thus, it is difficult to generate a desired frictional force. Accordingly, there has been a demand for a driving device enabled to drive a driven member with a simple configuration.
Also, in a case where a piezoelectric element deforms at a high rate in a related driving device, a frictional engagement member is somewhat pulled back together with a driving member, so that sometimes, vibrations of the piezoelectric element are not reliably transmitted.